Integrin signaling has been proposed to play a major role in the regulation of vascular smooth muscle cell (VSMC) behaviours. Proliferation of VSMCs requires the expression of CD98hc (4F2hc, SLC3A2), which is a membrane protein that is associated with amino acid transport and integrins. CD98hc is associated with cell proliferation in several different tissues but how CD98hc's functions relate to its role in proliferation has not yet been established. There are several studies that suggest a central role of integrins in CD98hc's ability to regulate cell proliferation. Furthermore, proliferation of VSMC is regulated through the ECM interaction, which are mainly mediated through integrins. To test whether CD98hc mediates integrin signaling to regulate the proliferation of VSMCs, I propose to first investigate which function of CD98hc regulates the proliferation of VSMCs. I will utilize a linked deletion and reconstitution strategy to characterize the regions of CD98hc that mediates proliferation. Mutants of CD98hc that affect either integrins or amino acid transporters have been identified previously. These mutants will thus enable me to establish the relative roles of the two interactions in VSMC responses. Mutations of the [unreadable]1 integrin that block CD98hc binding have also been previously identified. I will reconstitute [unreadable]1 null VSMCs with these mutants as a companion strategy to examine the role of integrin interactions in VSMC proliferation. Second I will determine the mechanism by which CD98hc regulates integrin-dependent signaling. I will examine the possible role of CD98hc oligomerization in integrin signaling by systematic mutagenesis of the extracellular and transmembrane domains of CD98hc to identify mutants that disrupt oligomerization and examine their effects on integrin signaling in VSMCs and in fibroblasts. As an alternative mechanism, I will test the possibility that CD98hc binds and therefore recruits key signaling intermediates to integrins. These studies will provide fundamental insight into the role of CD98hc in VSMC proliferation which is an important aspect of the pathogenesis of various diseases including atherosclerosis and post-angioplasty restenosis and may therefore represent a therapeutic target. VSMC proliferation contributes to the pathogenesis of many diseases such as atherosclerosis and post- angioplasty restenosis. The development of new therapeutic targets aimed at reducing vascular smooth muscle cell proliferation relies on studies such as this one that investigate the mechanism controlling vascular smooth muscle cell proliferation.